This invention relates to the reduction of decoding errors when using a flash analog to digital converter.
Telecommunications typically involves communicating a bit stream over a channel. At the sending end, the bit stream is typically encoded as an analog signal for transmission over the channel. At a receiver, the bit stream is decoded from the received analog signal. A real-world channel will impart distortions to the signal. It is the function of the receiver to endeavour to accurately recover the bit stream despite these distortions.
Where a bit stream is encoded as an analog modulated (AM) signal, at the receiver, after removal of any carrier wave, the signal may pass through an analog to digital decoder (ADC). One known type of ADC is a flash ADC which uses a set of 2n −1 comparators to directly measure the received analog signal to a resolution of n bits. For example, a three bit flash ADC will have seven comparators, each of which compares an input voltage with a different pre-set reference voltage level in order to “slice” the received analog voltage into one of eight levels. In use, the analogue input signal is sampled at a clock rate reflective of the bit rate of the bit stream on the channel. Each sample then represents one bit in the bit stream. For each sample, the voltage level of the sample inputs each comparator. The outputs from the comparators will indicate that the voltage of the sample lies between two reference voltages. In this way, the sample voltage may be digitised to the level of the lower of these two reference voltages. The digitised voltage then passes to an equaliser which attempts to address channel distortion in determining, based on the digitised voltage, whether the sample represents a binary 0 or a binary 1.
One significant cause of channel distortions results from temporal spreading of the signal when propagating over long distances or over nonlinear medium. This phenonenon is not effectively addressed by known equalisers. Therefore, the current invention seeks to provide an improved equalisation approach.